The present invention relates to a hydraulic valve head clearance eliminating device, that is called a hydraulic lash adjustor, in a valve operating mechanism for automatically eliminating valve head clearance in the latter with the aid of resilient force of a resilient member and hydraulic force and more particularly to an improved hydraulic lash adjustor which is capable of actuating the valve operating mechanism reliably and quietly for a long period of time and which has an excellently high durability.
There has been heretofore proposed a hydraulic lash adjustor of the above-mentioned type as illustrated in FIGS. 1 and 2. This construction is the subject of U.S. patent application Ser. No. 519,537 filed Aug. 1, 1983, now U.S. Pat. No. 4,530,319.
To facilitate understanding of the invention, the heretofore proposed device will first be described with reference to FIGS. 1 and 2.
As will be apparent from the drawings, a cylinder 1 serving as a housing for the hydraulic lash adjustor is constructed in a bottomed cylindrical configuration having an upper open end 1a and a closed lower end wall 1b, the cylinder 1 being firmly accommodated in a support hole Ea on an engine proper E. A plunger 2 having a semispherical end portion 2a at its upper end is slidably fitted into the cylinder 1, said semispherical end portion 2a projecting upwardly of the open end 1a of the cylinder 1. Further, the plunger 2 has a hydraulic oil reservoir chamber 4 formed therein and a bottom portion 5 at the lower end part while a cylindrical portion 11 is projected downwardly of the bottom portion 5 in a coaxial relation with respect to the plunger 2. On the inner wall surface of the cylindrical portion 11 is formed an annular engagement groove 14 having a rectangular cross-sectional configuration. The annular engagement groove 14 is located at a position spaced from the bottom portion 5 by a distance equal to or appreciably shorter than the thickness of flange portion 12b of a valve cage 12 which will be described later. A hydraulic chamber 3 is defined between the bottom portion 5 of the plunger 2 and the end wall 1b of the cylinder 1 and it is communicated with the hydraulic oil reservoir chamber 4 via a valve bore 5' formed through the bottom portion 5. The hydraulic oil reservoir chamber 4 is in communication with a hydraulic oil supply passage 10 via a through hole 6 on the side wall of the plunger 2, an annular hydraulic oil passage 7 between the sliding surfaces of the cylinder 1 and the plunger 2, a through hole 8 on the side wall of the cylinder 1 and an annular hydraulic oil passage 9 on the outer surface of the cylinder 1 so that the chamber 4 is normally filled with hydraulic oil delivered from the hydraulic oil supply passage 10.
The lower end of the cylindrical portion 11 of the plunger 2 serves as a stopper for limiting backward movement of the plunger 2 by abutting against a shoulder 1c formed on the inner side wall of the cylinder 1 at the lower end part thereof.
The valve cage 12 is accommodated in the hydraulic chamber 3. Specifically, the valve cage 12 comprises a cap-shaped main body 12a and the afore-mentioned flange portion 12b integrally extending radially outward from the peripheral end part of the main body 12a. The main body 12a has a through hole 13 formed therein, whereas the flange portion 12b is firmly held in position between the bottom portion 5 of the plunger 2 and a caulking ring 20 which is fitted into the annular engagement groove 14 by caulking operation.
A check valve 15 in the form of a ball is floatably accommodated in the valve cage 12 so as to open or close the valve bore 5'. The check valve 15 is adapted to open when hydraulic pressure in the hydraulic chamber 3 decreases and close when it increases and a stopper 16 is provided on the bottom of the valve cage 12 for limiting the working stroke of the check valve 15. Further, a coil spring 17 is accommodated in the hydraulic chamber 3 so as to force the plunger 2 to project upwardly of the cylinder 1.
The semispherical end part 2a of the plunger 2 abuts against the righthand end part of a rocker arm R as seen in the drawing to support the same, whereas the lefthand movable end part of the rocker arm R abuts against the valve head of a poppet valve V which serves to open or close an intake or exhaust port 18 of the internal combustion engine. To open or close the poppet valve V, a valve operating cam C is disposed at an intermediate part of the rocker arm R. The poppet valve V is provided with a valve spring S adapted to bias the valve in the closed position. It should be noted that resilient force of the valve spring S is set far stronger than that of the coil spring 17.
Next, operation of the prior art device will be described below.
When the poppet valve V is kept closed, the plunger 2 is raised up under the influence of resilient force of the coil spring 17 so that the righthand end part of the rocker arm R is biased upward until clearance between the lefthand end part of the rocker arm R and the valve head of the poppet valve V disappears. When hydraulic pressure in the hydraulic chamber 3 decreases as the plunger 2 is raised up, the check valve 15 is caused to open whereby hydraulic oil in the hydraulic oil reservoir chamber 4 is fed into the hydraulic chamber 3 through the valve bore 5' until the hydraulic chamber 3 is filled with hydraulic oil.
Next, when the cam face on the valve operating cam C comes in contact with the rocker arm R as it rotates, the intermediate part of the rocker arm R is depressed downward and valve opening force is developed so that hydraulic pressure appears in the hydraulic chamber 3 which has been kept closed by the check valve 15. Since the plunger 2 is held in the raised state under the influence of the thus developed hydraulic force, the rocker arm R is caused to turn about the semispherical end part 2a of the plunger 2 in the anticlockwise direction whereby the poppet valve V is opened against resilient force of the valve spring S. During the operation of the poppet valve V in that way an appreciable amount of hydraulic oil leakes from the hydraulic chamber 3 through close clearance between the sliding surfaces of the cylinder 1 and the plunger 2, but the leaked amount of hydraulic oil will be compensated by an auxiliary supply from the hydraulic oil reservoir chamber 4 during next closing operation of the poppet valve V.
Description will now be made as to how the valve cage 12 is firmly secured to the bottom portion 5 of the plunger 2. As schematically illustrated in FIG. 2, the flange portion 12b of the valve cage 12 is first brought in abutment against the lower surface of the bottom portion 5 of the plunger 2, the caulking ring 20 is then brought in abutment against the lower surface of the flange portion 12b and thereafter the caulking ring 20 is fitted into the annular engagement groove 14 by caulking operation with the aid of a caulking punch or the like tool. As a result the flange portion 12b of the valve cage 12 is firmly held in position between the bottom portion 5 and the caulking ring 20.
To assure that the caulking ring 20 is fitted into the annular engagement groove 14 with an intensity of locking force above a predetermined level, the caulking ring 20 is formed such that its lower surface is located below the lower side wall surface 14a of the annular engagement groove 14 by a distance H as shown in FIG. 2 prior to caulking into the groove 14. This distance H which represents an amount of overlapping between the caulking ring 20 and the annular engagement groove 14 varies within a certain range due to machining error and other factors.
When caulking operation is carried out at an insufficient caulking load with a large amount of overlapping H, there may be a case where the caulking ring 20 is subjected to plastic deformation while a part thereof is cut off by the corner edge of the lower side wall surface 14a of the annular engagement groove 14 because the surface 14a extends at right angles to the axis of the plunger 2. In this case, the caulking ring 20 tends to come in line contact or point contact with the lower side wall surface 14a of the annular engagement groove 14. This leads to an occurance of stress concentration on the contact area during operation.
On the other hand, when caulking operation is carried out at an insufficient caulking load with a small amount of overlapping H (with -H in an extreme case), a clearance may appear after mounting between the lower surface of the caulking ring 20 and the lower side wall surface 14a of the annular engagement groove 14 due to the rectangular cross-sectional configuration of the groove 14, which will cause the valve cage 12 to move up and down undesirably.
It should be noted that in either of both the above-mentioned cases the caulking ring 20 can be tightly fitted into the annular engagement groove 14 if caulking operation is carried out at a sufficiently high magnitude of caulking load. However, in that case, careful attention should be paid so that the flange portion 12b is held at a position between the bottom portion 5 of the plunger 2 and the caulking ring 20 during caulking operation and moreover, care should be taken so as not to damage or injure the valve cage 12 and the plunger 2 particularly in case of a small type hydraulic lash adjustor in which the cylindrical portion 11 of the plunger 2 has a very thin thickness at the position where the annular engagement groove 14 is formed.